1. Field of the Invention
The present invention relates to a panoramic imaging device.
2. Description of the Related Art
It is known to use an imaging device having an ultra-wide-angle optical system such as a fisheye lens to capture or take a panoramic image with a picture angle greater than 120° (degrees). However, the panoramic image captured by such imaging device is likely to have barrel distortion at periphery thereof. On the other hand, technologies have advanced to convert captured images to digital information, and process it. There are various imaging devices which have been developed to create a panoramic image based on such technologies, in which images in multiple picture-taking areas are captured by multiple optical systems positioned at predetermined angular positions for the respective picture-taking areas, and are combined into a panoramic image.
For example, an imaging device is known which uses three optical systems having lenses in front and on the left and right sides thereof, respectively, to form three images which are then electronically combined to form or reproduce a panoramic image with a picture angle of 180° (degrees) (refer to e.g. Japanese Laid-open Patent Publication 2005-26786). In order to form a panoramic image with a picture angle greater than 180°, two of the three optical systems in this imaging device uses very wide-angle lenses with a capture angle (or picture-taking angle) of 94.4°.
Thus, in order to form a panoramic image with a picture angle greater than 120° or 180° by using a small number of optical systems (lenses), it is necessary for a lens in an optical system to have a wide capture angle greater than 60°. This is advantageous because the small number of optical systems allows the imaging device to have a simple structure, thereby reducing the cost. However, this leads to a disadvantage in that images formed by using lenses having a capture angle greater than 60° are likely to have barrel distortions at peripheries thereof as described above, and that the barrel distortions cause unnatural transition between adjacent images in the panoramic image.
Normally, it is possible to digitally correct the barrel distortions at the peripheries of images. However, in the case where the images are captured by using wide-angle lenses having a capture angle much greater than 60° the images have larger barrel distortions, so that it is difficult to completely eliminate unnatural transition between adjacent images, and that complex programs are required to correct the barrel distortions. These problems are required to be solved. Furthermore, a panoramic imaging device of this kind should preferably be reduced in volume and thickness as much as possible, because a panoramic imaging device, for example, for capturing an image with a picture angle greater than e.g. 180° is mounted, in use, on a car body to image an area behind the car body, which is located in a dead angle of a driver.